Machining centers incorporating positioning devices such as turrets or carousels are well known in the art. Such positioning devices can take a variety of forms and the tool holders that are mounted on such devices can also assume different configurations. The efficiency afforded by the user of such positioning devices on machine centers is manifest in view of the ability of the machine to be programmed to perform numerous tasks using a variety of tools without the necessity of stopping the operation of the center to manually mount a specific tool on the spindle prior to each step in a machining operation. The individual tools can be mounted in tool holders in a variety of ways; further, the tool holders can be secured to the positioning means or carousel using a variety of techniques. One such tool holder configuration that may be used to hold tools on a carousel is shown in U.S. Pat. No. 3,999,769. In that patent, a tool holder is described that is mounted in a turret or carousel and is "locked" into position in the carousel until the tool that the holder is supporting is required for the machining operation. The carousel is then positioned beneath the spindle of the machine and the spindle is lowered into contact with the tool holder. The mechanism described in the above patent provides a means for the machine to automatically disengage the tool holder (and tool) fron the turret or carousel and to attach the holder to the spindle where it may be driven thereby and lowered so that the tool may come into contact with a work piece. Upon conclusion of the operation, the spindle is withdrawn and the tool holder is automatically replaced in the carousel and disengaged from the spindle.
Other techniques may be used to engage the machining center spindle and to disengage the spindle to replace the tool holder in the turret or carousel. Other devices are available in the prior art that can be attached to a machine tool such that the driving member or spindle drives the tool being held in the tool holder at an angle with respect to the spindle or at a velocity different than that of the spindle. However, these prior art devices are usually manually attached to the machine center and are secured in such a fashion that the machine must be stopped and the device completely removed before further operations are undertaken.